Impact of prédation upon honey bees (Hymenoptera, Apidae), by orb‐weaving spiders (Araneae, Araneidae and Tetragnathidae) in grassland ecosystems

Estimates of prédation on the honey bee, Apis mellifera L., by a guild of orb‐weaving spiders were made in two different habitats in central Europe. In the first habitat, an abandoned grassland (megaphorbe meadow), honey bees comprised 1 % (by numbers) of the 7480 prey items collected from orb‐webs between May and September. Approximately 99 % of the 72 observed cases of prédation on honey bees took place in the second half of summer (August‐September), when the three large orb‐weaver species Argiope bruennichi (Scopoli), Araneus quadratus Clerck and Araneus diadematus Clerck reached full size (matured) and built large, strong (ca. 25 cm diameter) webs. Prédation by these spider species on honey bees in the first half of summer was apparently insignificant (only 1 % of observed prédation events), probably due to their relatively small web and body size. Based on sampling counts of the number of webs per m² and the number of bees intercepted per web, we estimated that the spiders' prey kill per m² in the grassland averaged 1 honey bee every 4th day in August, and 1 every 5th day in September during rain free periods. About 95 % of observed orb‐weaver prédation was attributable to A. bruennichi and A. quadratus, while 5 % was due to A. diadematus. The second estimate was made in another abandoned grassland habitat, heavily infested with the thistle Cirsium arvense (L.), in the same geographic area. Honey bees comprised 15 % (by numbers) of 215 prey items collected from webs of the dominant orb‐weaver species (A. bruennichi) during August‐September. We estimated that the A. bruennichi population may have killed approximately 1 honey bee per m² every 5th day in August during rain free periods. The economic status of orb‐weaving spiders as predators is discussed, and we conclude that despite their activities in killing beneficial arthropods, these spiders should not be addressed as pests. Should bee keepers feel their hives are threatened, relatively innocuous cultural methods can be used in place of hazardous chemicals in the neighborhood of the hive that destroy the orb‐weavers' web‐sites in the grassland (mowing).